Use release disambiguation not release-group disambiguation. I found 2 examples why I would prefer the release disambiguation:   http://musicbrainz.org/release-group/d3f057b4-7e89-3018-9f84-9835ed9b4732   http://musicbrainz.org/release-group/6792b6d1-4e65-3c3c-9d20-d08aa1dcfc60 I did not find an example where the release-group disambiguation would be important (of course, that doesn't prove anything ;))
Use release disambiguation not release-group disambiguation.
I found 2 examples why I would prefer the release disambiguation:
  http://musicbrainz.org/release-group/d3f057b4-7e89-3018-9f84-9835ed9b4732
  http://musicbrainz.org/release-group/6792b6d1-4e65-3c3c-9d20-d08aa1dcfc60
I did not find an example where the release-group disambiguation would be important (of course, that doesn't prove anything ;))
bj-yinyan/beets,bj-yinyan/beets,lengtche/beets,swt30/beets,pkess/beets,mried/beets,mosesfistos1/beetbox,diego-plan9/beets,shamangeorge/beets,mathstuf/beets,ibmibmibm/beets,kelvinhammond/beets,kareemallen/beets,ibmibmibm/beets,arabenjamin/beets,SusannaMaria/beets,lightwang1/beets,tima/beets,ruippeixotog/beets,madmouser1/beets,m-urban/beets,PierreRust/beets,imsparsh/beets,Dishwishy/beets,Freso/beets,Freso/beets,parapente/beets,multikatt/beets,PierreRust/beets,multikatt/beets,parapente/beets,bj-yinyan/beets,mosesfistos1/beetbox,sadatay/beets,kareemallen/beets,jcoady9/beets,jmwatte/beets,sampsyo/beets,MyTunesFreeMusic/privacy-policy,ibmibmibm/beets,bj-yinyan/beets,drm00/beets,jmwatte/beets,ttsda/beets,asteven/beets,Wen777/beets,krig/beets,Kraymer/beets,mathstuf/beets,YetAnotherNerd/beets,ruippeixotog/beets,multikatt/beets,Andypsamp/CODfinalJUNIT,andremiller/beets,dfc/beets,marcuskrahl/beets,Kraymer/beets,artemutin/beets,shamangeorge/beets,Kraymer/beets,arabenjamin/beets,drm00/beets,asteven/beets,pkess/beets,dfc/beets,randybias/beets,jmwatte/beets,diego-plan9/beets,m-urban/beets,gabrielaraujof/beets,sadatay/beets,shanemikel/beets,mried/beets,swt30/beets,sadatay/beets,Dishwishy/beets,untitaker/beets,imsparsh/beets,madmouser1/beets,m-urban/beets,tima/beets,Andypsamp/CODjunit,lengtche/beets,lightwang1/beets,tima/beets,MyTunesFreeMusic/privacy-policy,kelvinhammond/beets,shanemikel/beets,imsparsh/beets,andremiller/beets,beetbox/beets,jackwilsdon/beets,lengtche/beets,jcoady9/beets,SusannaMaria/beets,Andypsamp/CODjunit,moodboom/beets,asteven/beets,parapente/beets,jmwatte/beets,Freso/beets,untitaker/beets,lightwang1/beets,Wen777/beets,jbaiter/beets,ruippeixotog/beets,ttsda/beets,marcuskrahl/beets,andremiller/beets,sampsyo/beets,YetAnotherNerd/beets,jcoady9/beets,dfc/beets,randybias/beets,swt30/beets,tima/beets,shamangeorge/beets,ttsda/beets,moodboom/beets,shanemikel/beets,PierreRust/beets,beetbox/beets,LordSputnik/beets,randybias/beets,Andypsamp/CODjunit,kareemallen/beets,Freso/beets,xsteadfastx/beets,Andypsamp/CODfinalJUNIT,jayme-github/beets,YetAnotherNerd/beets,marcuskrahl/beets,sadatay/beets,xsteadfastx/beets,MyTunesFreeMusic/privacy-policy,ruippeixotog/beets,jackwilsdon/beets,mried/beets,Kraymer/beets,gabrielaraujof/beets,Wen777/beets,xsteadfastx/beets,swt30/beets,marcuskrahl/beets,LordSputnik/beets,kelvinhammond/beets,gabrielaraujof/beets,pkess/beets,Andypsamp/CODjunit,shanemikel/beets,jcoady9/beets,imsparsh/beets,mosesfistos1/beetbox,diego-plan9/beets,arabenjamin/beets,pdf/beets,sampsyo/beets,PierreRust/beets,moodboom/beets,m-urban/beets,jackwilsdon/beets,arabenjamin/beets,drm00/beets,madmouser1/beets,pkess/beets,gabrielaraujof/beets,artemutin/beets,LordSputnik/beets,jbaiter/beets,SusannaMaria/beets,madmouser1/beets,multikatt/beets,randybias/beets,kareemallen/beets,jackwilsdon/beets,sampsyo/beets,xsteadfastx/beets,artemutin/beets,LordSputnik/beets,jayme-github/beets,beetbox/beets,pdf/beets,lightwang1/beets,Andypsamp/CODfinalJUNIT,mried/beets,Andypsamp/CODjunit,mathstuf/beets,mathstuf/beets,krig/beets,untitaker/beets,YetAnotherNerd/beets,untitaker/beets,Andypsamp/CODfinalJUNIT,Dishwishy/beets,krig/beets,asteven/beets,SusannaMaria/beets,moodboom/beets,lengtche/beets,shamangeorge/beets,kelvinhammond/beets,ibmibmibm/beets,MyTunesFreeMusic/privacy-policy,Andypsamp/CODfinalJUNIT,diego-plan9/beets,beetbox/beets,ttsda/beets,parapente/beets,artemutin/beets,Dishwishy/beets,mosesfistos1/beetbox,drm00/beets,dfc/beets